DE1946035A1 - Circuit arrangement for supplying high voltage to the end anode of a display tube - Google Patents

Description

PHB. 31,307

Dipping. ERICH E. WALTHER j # / vjm. .-

abrieken

Registration from: / (/ / '> c 7

. Y

"Circuit arrangement for the supply of high voltage to the sndanoäe of a display tube ".

The invention relates Si ¹ Ch to a circuit arrangement in law supply of high voltage to the prices comply _v anode of a picture tube in a picture display.

s « direction, which ait a line output transformer« a \

> ■ V '

High voltage winding on the core of this transformer ^ un \ J

one through capacitors and riding in only one direction

V -

Elenente trained multiplication circuit provided let, which is connected to the terminals of the high voltage winding, thus the voltage peaks occurring on this winding are multiplied and the multiplied voltage is rectified.

One such method, high voltage

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HAD ORIGiNAL

PIiH. ; n.9i> 7.

■ "2 ··

to produce has long been known. It is described for example in the book "Television" from F.Kerkhof and W.Werner, 2nd Edition (195 ¹ O in ^the figures 7.3-2 (page 216) and 7.3-8 (s. 22 ≠ 0. The input power a color display tube is large, namely in the order of magnitude of ho W. The control of the high voltage must be good, otherwise the color purity with large beam currents would deteriorate due to the decrease in the high voltage. The greater the internal resistance of the high voltage generator, the greater it is Decrease in high voltage with increasing beam current. In particular with high powers, this internal resistance must then be small for good regulation. In addition, if the internal resistance of the high voltage source is high, the high voltage will be lower, and thus the light yield will not be as high as in the case of a Small internal resistance. Due to a large internal resistance, the reproduced picture can "breathe" due to the fluctuations in the recorded Ββα jet stream, ie the dimensions of the image can change, the high voltage decreases when the beam current increases. The internal resistance can be reduced by using a multiplier circuit. It turns out, however, that the internal resistance obtained in this way is greater at low jet currents than at high jet currents.

It is obvious to this problem

loosen themselves by creating a resistance across the terminals the high voltage source is switched, so that a

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Current of at least 20O / uA is always taken from the multiplier circuit, while oscillations occurring in the high voltage, the origin of which will be explained in more detail, are cut off at the same time. However, because the high voltage required for the end anode is 25 kV in color display tubes, this would require an expensive chain of a large number of well-insulated resistors. A better solution would be a voltage-dependent resistor instead of the chain mentioned, but such an element takes up a lot of space. A so-called ballast tube can also be used. A disadvantage of the pointless loss of power, however, remains while such a tube is not free from X-rays, which requires a sheath. The aim of the invention is to solve the problem mentioned in a simple manner, without the need for an additional current to be drawn off, and is characterized in that a load circuit consisting of at least one diode in series with the parallel connection of a resistor and a capacitor is connected between the Terminals of the high-voltage winding is connected, and that the diode is given such a conductivity direction that oscillations occurring on the winding mentioned, which have an opposite polarity to the pulses occurring during the line retrace, are cut off.

It should be noted that it has become common practice to tune ZI output transformers to frequencies from

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4 -

one of which is the flyback frequency and the other approximately is an odd harmonic thereof. Such a vote is in the German patent specification 977 * 115 , (PH. 11497) and in the German patent application P 1805499.4 (PHN. 28O1). By tuning to the so-called fifth harmonic, there is already a small internal resistance the high voltage source obtained by the The peaks of the high-voltage pulses to be rectified have become flatter. As a result, the picture "breathes" less when it is the recorded beam current changes. However, since the aforementioned type of voting is never completely ideal, you can immediately on Oscillations still occur at the beginning of the line trace time.

An embodiment of the invention is

shown in the drawing, and is described in more detail below. Show it:

Fig. 1 shows a multiplication circuit of the known one Type, i.e. a tripler,

Fig. 2 shows a shape of the input voltage of Circuit arrangement according to Fig. 1,

3 shows an embodiment of the inventive Circuit arrangement »

In Fig. 1, the terminal A is with the on her

other side earthed high-voltage winding of the line output transformer, at which the peak-to-peak amplitude of the voltage of the occurring during line retrace positive impulse has a value of, for example, 8.4 kV hai, tied together. Between terminal A and earth is <Aio Roihon-

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circuit of a diode D and a capacitor C, vvobo i the anode of the diode D _{1 is} connected to the terminal A. During the flyback periods, the capacitor C. auV the maximum value of the voltage present at the terminal A; charged. During the line trace periods _{the capacitor C "is charged via the diode D 0} by the positive potential of the capacitor C ₁ , because the terminal A is then almost at ground potential. When the line return pulses occur, voltage pulses are applied across the capacitor C" the diode D_ placed, but superimposed on the DC voltage potential present at the terminals of this capacitor. As a result, the capacitor C ~ is charged up to twice the value of the input pulse at terminal A. Similarly, during the line trace periods, the capacitor C, via the diode D, is charged up to the DC voltage potential at the capacitor C_, while in the flyback periods voltage pulses via D are applied to the stray capacitance C_ of the picture display tube, the potential at C _{r being} around the DC voltage potential at Capacitor C. is increased. These pulses are rectified by the diode D_ and the capacitor C_ is charged to a potential, that is to say the high-voltage potential which corresponds approximately to three times the amplitude of the voltage pulse at the input of the circuit.

Fig. 2 shows the waveform present at terminal A during the run-out and return periods, in which the above-mentioned oscillations ⁰ ^ beginning of the run-

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PHB. 31,907.

. times are given,

During the line retrace time, diodes D ₁ , D_ and D are _{conducting at time t 1} (FIG. 2), while diodes D "and D. are conducting during the outward run, which begins at time t". The ratio of the conduction times of the said diodes depends on the high-voltage power drawn by the display tube. When the beam current is low, the diodes rectify the full amplitudes between points a and b of the waveform in FIG. If the beam current now exceeds the value of about 200 / uA, the oscillations shown in FIG. 2 after the time tp are cut off, but the high voltage decreases by at least 2kV as a result. Once these oscillations are cut off, the high voltage rams only a little if the beam current increases further.

FIG. 3 is an illustration of an exemplary embodiment of the circuit arrangement according to the invention, corresponding elements from FIG. 1 being indicated with the same reference numerals. Between terminal A, which is the live end of the high-voltage winding of a line output transformer (not shown in the figure), and earth, the series connection of a resistor R ₁ and a diode D is connected in such a way that the anode of the diode D is connected to Earth is connected. The resistance

R «is through a capacitor C> and the diode D, - through j ο ο

the .series circuit of a resistor R "and a capacitor C _n , bridged. · ·

7 ·

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If the voltage at terminal A is negative

When the voltage decays, the diode D ^ conducts, whereby a current flows through the parallel connection of the capacitor C ^ and the resistor R ₁ , so that the negative decay voltage is cut off and therefore cannot contribute to the high voltage that is generated at the capacitor C_ If the beam current is small and the beam current is large, the generated high voltage will have almost the same value.

Because of the capacitor C, - arises at the

Cathode of the diode D ^ a positive voltage which is _{further smoothed by the series connection of the resistor R 2} and the capacitor C_. The first acceleration anode of a color picture display tube of the shadow mask type requires a voltage of the order of magnitude of 7 to 80 V. This voltage can advantageously be supplied by the DC voltage present _{on the capacitor C 7.} In the case of line output stages which are formed with semiconductors, it is customary to use a separate peak rectifier in order to obtain this voltage, and this separate rectifier can be dispensed with thanks to the measure mentioned above.

The focusing electrode of a color display tube of the shadow mask type needs a potential which is approximately 5 kV and which can be derived by means of a voltage divider between the high voltage and earth or from a tap of the line output transformer. This voltage can now be measured by means of a potentiometer connected in parallel to _{the capacitor C 1 of the multiplication circuit}

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V derive. The little stream that runs through this Po tojii ioine - R

ters flows, also contributes to smoothing the tip of the line return impulse in Fig. 2, which is a further reduction caused by the internal resistance of the high voltage source.

By choosing the ratio of capacitors

Acts of the capacitors C ^ and C "can be defined a certain

ο 2

The extent to which the circuit located on the left-hand side of point A in FIG. 3 is secured against a possible breakdown in the picture display tube. If such a breakdown occurs, the high-voltage line, d-rtw the capacitor C_, is short-circuited to earth. As a result, the charge of the capacitors C ₁ , C "and C flows through the diodes D _p , D. and D_ vreg. Because the diode D ₁ is blocked, however, the charge of the capacitor C "can find no other way than the high-voltage winding via the terminal A. The voltage at the capacitor C ₁ is almost zero, which creates a" negative current pulse at the input of the tripler circuit. A measured value was about 10A, which can cause damage to the row output transistor. However, if the voltage on the capacitor Cp becomes more negative than the voltage on the C ^, the diode D will slide and the capacitors C ₂ and Cg 'form a capacitive voltage divider, as a result of which only a small part of the voltage of the terminal a caused by the breakdown fed w ± rd _f if the capacitance of the capacitor Cg is made much larger than that of the capacitor C ". In this way, the line output transistor is secured to some extent.

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PHB. 31,907.

Another measure can be admission

of a resistor R- between the capacitor C. and earth, whaturbh the discharge current through this capacitor is decreased. One chooses a value for the resistance R_, for example 470 ohms, which is much larger than that of the Discharge path across the display tube, i.e. about 50 ohms. If a breakdown occurs, a negative one arises

becomes conductive.

The capacitor CV can therefore discharge, which is another brings better protection of the line output transistor with it.

In one embodiment of the invention Circuit the following parts were used.

Capacitors C _1, C, C "and C ^, tripler LP

¹ * ^J 1174

Voltage across resistor R ", which causes the diode

Diodes D ₁ , D, D_, D ^ and D.

1174

(Mullard Ltd.)

Capacitor C.

Capacitor C,

Diode D,

Resistance R

Resistance R,

: 1 nF

: 1 nF

: Mullard, type BY: 500 kOhm.

; 10 MOhm.

009810/1243

Claims (1)

. PHB. 31,907. - 10 • PA TENTANS PRUCHE . . Circuit arrangement for the delivery of high voltage to the end anode of a picture display tube in a Image display device using a line output transformerij , a high voltage winding on the core of this transformer, one through capacitors and in only one Direction of conductive elements formed multiplication circuit is provided, which is connected to the terminals of the high-voltage winding is connected to multiply the voltage peaks occurring on this winding and for rectification the multiplied voltage, characterized in that one of at least one diode in series with the parallel connection a resistor and a capacitor existing load circuit between the terminals of the high-voltage winding is switched, and that the diode is given such a conductivity direction that at said Winding oscillations that occur compared to the during of the line rewind occurring pulses an opposite one Show polarity, be cut off " 2. Circuit arrangement according to claim 1, characterized in that the picture display tube is a color display tube is. 3. Circuit arrangement according to one of the preceding Claims, characterized in that a positive supply voltage for an anode of the picture display tube, the Connection point of the resistor, the capacitor and the diode is taken. ■ ' 009816/1246 ^v -. 'PHB. 31.90 ?. - 1 1 - k. Circuit arrangement according to one of the preceding claims, characterized in that the multiplication circuit is a tripling circuit. 5. Circuit arrangement according to one of the preceding Claims, characterized in that the capacitor has a much larger capacity than the first capacitor in the multiplication circuit. 6. Circuit arrangement according to one of the preceding Claims, characterized in that a resistor in the series connection of one of the capacitors and one the unidirectional conductive elements of the multiplier circuit connected to the terminals of the high-voltage windings is recorded. 00981 6/1248